The present invention relates to a composition which is capable of imparting improved fluid loss controlling properties to aqueous systems. More particularly, the present invention relates to the formation of an improved water-based drilling fluid containing the subject composition and to an improved method of drilling bore holes into subterranean formations using said drilling fluid.
In normal well drilling operations in which a well is drilled by a rotary method, the well bore hole is generally filled with a drilling fluid or mud which is circulated therein. Drilling fluids are usually pumped down through the drill stem of the rotary rig, circulated around the drill bit and returned to the surface through the annular passage between the drill stem and well wall. These drilling fluids perform a number of functions including lubricating the drill stem and bit, cooling the bit, carrying the cuttings from the bit up the bore hole to the surface where the cuttings may be separated and disposed of, and providing a hydrostatic head against the walls of the well to contain downhole geopressure.
Various clay or colloidal clay bodies such as bentonite, sepiolite, attapulgite and the like have been used in drilling fluids for many years. The use of these materials has caused the industry to refer to drilling fluids as "muds."
The drilling fluid must be capable of resisting the loss of fluid, normally water, into the porous strata through which the bore hole traverses. The loss of fluid causes the formation and build-up of a cake deposit which, after a period of time, can result in the sticking of the drill pipe and stoppage of the drilling operation. The fluid must, therefore, be of a nature which permits minimum loss into the porous strata. Agents which impart such property are conventionally termed "water loss controllers" or "fluid loss controllers."
The drilling fluid must be capable of exhibiting the above-described fluid-loss properties under changing composition and environmental conditions encountered during the drilling operation. The drilling fluid components should be substantially stable to the presence of various calcium compounds as well as sodium chloride which may be present in the fluid from the soil strata with which it is in contact and/or due to the use of salt water having calcium or sodium salts therein used in forming the drilling fluid.
It is also desired that the agents contained in conventional drilling fluids are stable and functional at elevated temperature. It is well known that as the bore hole increases in depth the temperatures encountered are substantially above that found at the earth's surface. Further, heat is generated by frictional forces on the drill bit. It is, therefore, desired that components used in forming drilling fluids be stable and functional at varying elevated temperature conditions.
The increased filtrate viscosity caused by the viscosifying agent of a drilling fluid has been relied upon as a mode of aiding in fluid loss control with little success especially when drilling into and through microporous formations. To further enhance the control, various agents have been added. For example, in U.S. Pat. No. 3,032,498 a cyanoethylated starch was described as a water loss controller when used in combination with a clay-based mud. U.S. Pat. No. 3,988,246 describes an esterified or etherified starch as a water loss controlling agent when combined with a xanthan gum based drilling mud. Other starches have been employed in clay free muds under limiting temperature conditions as starches are known to be temperature sensitive.
Bentonite clays which have sodium as the major exchangeable ion, such as Wyoming bentonite, have been used to impart fluid loss controlling properties to drilling fluids. These bentonites must be used in large dosages to approach practical fluid loss properties and usually impart fluid loss which is still higher than desired by the industry. Bentonite clays which have calcium or magnesium as the major exchangeable ion have been used to impart rheological properties to drilling muds, but these clays are not capable of imparting fluid loss properties.
There is a need for a method for imparting a high degree of fluid loss inhibiting properties to solid particulate silicate or alumino-silicate materials contained in aqueous compositions such as drilling fluid compositions. The properties of the composition should be stable to varying conditions and temperatures commonly encountered in drilling operations.